Bi4O5Br2 Nanoflower and CdWO4 Nanorod Heterojunctions for Photocatalytic Synthesis of Ammonia

In this study, a Bi4O5Br2/CdWO4 (BOB/CWO) composite photocatalyst was designed and prepared using a convenient hydrothermal method. A detailed investigation was carried out on the morphology, specific surface area, structure, optical properties, and photoelectric chemical properties of the BOB/CWO composite. The CdWO4 nanorods were found to disperse on the surface of Bi4O5Br2 nanoflowers, and their tight contact between CdWO4 and Bi4O5Br2 resulted in the formation of a heterojunction structure. By analysis of the band structure of the two semiconductors, it was found that the heterojunction worked in a type II mechanism, effectively improving the separation efficiency of electron–hole pairs. Therefore, the BOB/CWO composite exhibited high performance in photocatalytic N2 fixation (PNF) reactions. The optimal BOB/CWO catalyst presents a PNF rate of 501 μmol L–1 g–1 h–1 under simulated sunlight irradiation, which was 5.7 and 3.1 times that of pure CdWO4 and Bi4O5Br2, respectively. Under visible-light illumination, the BOB/CWO heterojunction worked in a sensitized mechanism, and the coupling effect of CdWO4 and Bi4O5Br2 in boosting the PNF reaction could still be observed. The findings of this study are anticipated to offer practical knowledge about the design and synthesis of efficient photocatalysts for PNF.